Device and system for power transmission

ABSTRACT

A device for power transmission includes a power transmission section and a detection section. The power transmission section is configured to transmit an electric power wirelessly. The detection section is operatively connected to the power transmission section and configured to detect an object within a range from the power transmission section based on a change in impedance in vicinity of the power transmission section.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 14/343,737, filed Mar. 7, 2014, which is a NationalStage of PCT/JP2012/068546, filed Jul. 17, 2012, and claims the priorityfrom prior Japanese Priority Patent Application JP 2011-197865 filed inthe Japan Patent Office on Sep. 12, 2011. Each of the above-referencedapplications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a system that performs noncontact power supply(electric power transmission) to a device to be power-supplied (anelectronic device and the like), and a device applied to such a system.

BACKGROUND

In recent years, attention has been given to a feed system (a noncontactfeed system or a wireless charging system) that performs noncontactpower supply (electric power transmission) to a CE device (ConsumerElectronics Device) such as a portable telephone or a portable musicplayer. This makes it possible to start the charge merely by placing anelectronic device (a secondary-side device) on a charging tray (aprimary-side device), instead of starting the charge by inserting(connecting) a connector of a power-supply unit such as an AC adapterinto the device. In other words, terminal connection between theelectronic device and the charging tray become unnecessary.

As a method of thus performing noncontact power supply, anelectromagnetic induction method is well known. In recent years, anoncontact feed system using a method called a magnetic resonance methodhas also been receiving attention. Such noncontact feed systems aredisclosed in PTLs 1 to 3, for example.

CITATION LIST Patent Literature

-   PTL1: Japanese Patent No. 3179802-   PTL2: Japanese Unexamined Patent Application Publication No.    2008-167582-   PTL3: Japanese Unexamined Patent Application Publication No.    2010-119251

SUMMARY OF INVENTION

Incidentally, in a noncontact feed system like those described above,when a feed unit (a primary-side device) is not allowed to determinewhether a device to be power-supplied (a secondary-side device) is inproximity (close to the feed unit; in a region where power feeding ispossible, for example), the feed unit keeps supplying the power, therebycausing wasteful power consumption.

Here, PTLs 1 to 3 each propose a technique of detecting whether a deviceto be power-supplied is in proximity to a feed unit. However, there is adisadvantage of lacking in convenience because, for example, aconfiguration, a technique, and the like are complicated.

Therefore, suggestion of a technique capable of conveniently detecting adevice to be power-supplied at the time of electric power transmission(noncontact power feeding) using a magnetic field has been expected.

It is desirable to provide a device and a system capable of convenientlydetecting a device to be power-supplied when electric power transmissionis performed using a magnetic field.

A device for power transmission according to an embodiment of thedisclosure includes a power transmission section configured to transmitan electric power wirelessly, and a detection section operativelyconnected to the power transmission section and configured to detect anobject within a range from the power transmission section based on achange in impedance in vicinity of the power transmission section.

A system for power transmission according to an embodiment of thedisclosure includes a transmitting device and a receiving device. Thetransmitting device includes a power transmission section configured totransmit an electric power wirelessly and a detection sectionoperatively connected to the power transmission section and configuredto detect a receiving device within a range from the power transmissionsection based on a change in impedance in vicinity of the powertransmission section. The receiving device includes a power receptionunit configured to receive the electric power wirelessly, and a loadoperatively connected to the power reception unit and configured toperform an operation based on the received electric power.

In the device and the system for power transmission according to theembodiments of the disclosure, whether the device to be power-suppliedby the power transmission section is in proximity or not is detectedusing the change in the impedance in the vicinity of the powertransmission section. This makes it possible to perform detection of thedevice to be power-supplied without complicating a configuration and atechnique, for example.

According to the device and the system for power transmission of theembodiments of the disclosure, whether the device to be power-suppliedby the power transmission section is in proximity or not is detectedusing the change in the impedance in the vicinity of the powertransmission section. Therefore, it is possible to perform detection ofthe device to be power-supplied without complicating a configuration anda technique, for example. Hence, it is possible to detect the device tobe power-supplied conveniently when the power transmission section isperformed using the magnetic field.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thetechnology.

FIG. 1 is a perspective diagram illustrating an appearance configurationexample of a feed system according to a first embodiment of thedisclosure.

FIG. 2 is a block diagram illustrating a detailed configuration exampleof the feed system depicted in FIG. 1.

FIG. 3 is a circuit diagram illustrating a detailed configurationexample of part of blocks depicted in FIG. 2.

FIG. 4 is a flowchart illustrating an operation example of a feed unitaccording to the first embodiment.

FIG. 5 is a timing chart illustrating an example of a detection periodand a non-detection period for detection of a secondary-side device.

FIGS. 6A and 6B are characteristic diagrams used to explain a change inimpedance characteristics in response to the presence or absence of thesecondary-side device and a metallic foreign object.

FIG. 7 is a diagram illustrating timing waveforms each representing anexample of a control signal for a high-frequency power generationcircuit.

FIGS. 8A and 8B are characteristic diagrams used to explain a change inharmonic component corresponding to a duty ratio of the control signal.

FIG. 9 is a characteristic diagram used to explain a change in impedancecharacteristics in response to a change in the harmonic component.

FIG. 10 is a timing chart illustrating an example of a power feedingperiod and a communication period.

FIG. 11 is a block diagram illustrating a configuration example of afeed system according to a second embodiment.

FIG. 12 is a flowchart illustrating an operation example of a feed unitaccording to the second embodiment.

FIGS. 13A and 13B are timing charts illustrating a detection period anda non-detection period according to modifications 1 and 2.

FIGS. 14A and 14B are timing charts illustrating a detection period anda non-detection period according to modifications 3 and 4.

FIGS. 15A and 15B are timing charts illustrating a detection period anda non-detection period according to modifications 5 and 6.

DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure will be described below in detail withreference to the drawings. It is to be noted that the description willbe provided in the following order.

1. First embodiment (an example using impedance determined from analternating current and an AC voltage)

2. Second embodiment (an example using direct-current resistancedetermined from a direct current and a DC voltage).

3. Modifications common to the first and second embodiments

Modifications 1 and 2 (examples each using a plurality of kinds of valuefor a frequency of a control signal)

Modifications 3 and 4 (examples each using a plurality of kinds of valuefor a duty ratio of the control signal)

Modifications 5 and 6 (examples each using a plurality of kinds of valuefor the frequency and the duty ratio of the control signal)

4. Other modifications

First Embodiment

[Overall Configuration of Feed System 4]

FIG. 1 illustrates an appearance configuration example of a feed system(a feed system 4) according to the first embodiment of the disclosure,and FIG. 2 illustrates a block configuration example of this feed system4. The feed system 4 is a system (a noncontact-type feed system) thatperforms electric power transmission (power supply, or power feeding) ina noncontact manner by using a magnetic field (by using electromagneticinduction, magnetic resonance, or the like, for example; likewisehereinafter). This feed system 4 includes a feed unit 1 (a primary-sidedevice) and one or a plurality of electronic devices (here, twoelectronic devices 2A and 2B; secondary-side devices) each serving as adevice to be power-supplied.

In this feed system 4, electric power transmission from the feed unit 1to the electronic devices 2A and 2B is performed by placing theelectronic devices 2A and 2B on (or brought close to) a power feedingsurface (a power transmission surface) S1 in the feed unit 1, asillustrated in FIG. 1, for example. Here, in consideration of a casewhere the electric power transmission to the electronic devices 2A and2B is performed simultaneously or time-divisionally (sequentially), thefeed unit 1 is shaped like a mat (a tray) in which the area of the powerfeeding surface S1 is larger than the electronic devices 2A and 2B to besupplied with the power.

(Feed Unit 1)

The feed unit 1 is a unit (a charging tray) that performs the electricpower transmission to the electronic devices 2A and 2B by using amagnetic field as described above. This feed unit 1 includes a powertransmission unit 11 having a power transmission section 110, a powercircuit 111, a high-frequency power generation circuit (an AC signalgeneration circuit) 112, a current-voltage detection section 113, acontrol section 114, and a capacitor C1 (a capacitive element) asillustrated in FIG. 2, for example. Of these, the current-voltagedetection section 113 and the control section 114 correspond to aspecific example of a “detection section” of the disclosure, and thecontrol section 114 corresponds to a specific example of a “controlsection” of the disclosure.

The power transmission section 110 is configured to include a powertransmission coil (a primary-side coil) L1 to be described later, andthe like. The power transmission section 110 uses the power transmissioncoil L1 and the capacitor C1, thereby performing the electric powertransmission to the electronic devices 2A and 2B (specifically, a powerreception section 210 to be described later) through use of the magneticfield. Specifically, the power transmission section 110 has a functionof emitting a magnetic field (a magnetic flux) from the power feedingsurface S1 to the electronic devices 2A and 2B. It is to be noted that aconfiguration of this power transmission section 110 will be describedlater in detail (FIG. 3).

The power circuit 111 is, for example, a circuit that generates apredetermined DC voltage based on electric power (AC power or DC power)supplied from a power supply source 9 external to the feed unit 1, andoutputs the generated DC voltage to the high-frequency power generationcircuit 112. Such a power circuit 111 is configured to include, forexample, a DC-DC converter or an AC-DC converter. It is to be noted thatthis power circuit 111 may not be provided in some cases.

The high-frequency power generation circuit 112 is a circuit thatgenerates predetermined high-frequency electric power (an AC signal)used to perform the electric power transmission in the powertransmission section 110, based on the DC voltage outputted from thepower circuit 111. Such a high-frequency power generation circuit 112 isconfigured using, for example, a switching amplifier to be describedlater. It is to be noted that a configuration of this high-frequencypower generation circuit 112 will also be described later in detail(FIG. 3).

The current-voltage detection section 113 has a current detectionsection 113I and a voltage detection section 113V which will bedescribed later, and detects an alternating current (a current I1) andan AC voltage (a voltage V1) in the vicinity of the power transmissionsection 110 (here, on a load side of the high-frequency power generationcircuit 112), respectively. It is to be noted that a configuration ofthis current-voltage detection section 113 will also be described laterin detail (FIG. 3).

The control section 114 has a function of controlling operation of eachof the power circuit 111 and the high-frequency power generation circuit112. Specifically, the control section 114 drives the high-frequencypower generation circuit 112 by using a control signal CTL having apredetermined frequency and a predetermined duty ratio, as will bedescribed later in detail. Further, the control section 114 also has afunction of detecting whether or not a device (the secondary-sidedevice; here, the electronic devices 2A and 2B) to be supplied withpower by the power transmission section 110 is in proximity (in thevicinity of the power feeding surface S1; for example, in a region wherepower feeding is possible, likewise hereinafter), based on the currentI1 and the voltage V1 detected in the current-voltage detection section113. Specifically, as will be described later in detail, this controlsection 114 detects the device to be power-supplied by using a change inimpedance (here, a load impedance of the high-frequency power generationcircuit 112 (the switching amplifier to be described later)) in thevicinity of the power transmission section 110. Here, this loadimpedance is impedance of a load connected to the switching amplifier tobe described later, and is determined by the alternating current (thecurrent I1) and the AC voltage (the voltage V1) described above. It isto be noted that such a control section 114 is, for example, amicrocomputer or the like.

The capacitor C1 is disposed to be connected to the power transmissioncoil L1 electrically in parallel or in a combination of parallel andseries.

(Electronic Devices 2A and 2B)

The electronic devices 2A and 2B are, for example, stationary electronicdevices represented by television receivers, portable electronic devicescontaining a chargeable battery (battery) represented by portabletelephones and digital cameras, and the like. As illustrated in, forexample, FIG. 2, these electronic devices 2A and 2B each include a powerreception unit 21, and a load 22 that performs predetermined operation(operation of performing functions of serving as the electronic device)based on electric power supplied from this power reception unit 21.Further, the power reception unit 21 includes the power receptionsection 210, a rectifying and smoothing circuit 211, a voltagestabilizing circuit 212, and a capacitor (a capacitive element) C2.

The power reception section 210 is configured to include a powerreception coil (a secondary-side coil) L2. The power reception section210 has a function of receiving electric power transmitted from thepower transmission section 110 in the feed unit 1 by using this powerreception coil L2 and the capacitor C2. It is to be noted that aconfiguration of this power reception section 210 will also be describedlater in detail (FIG. 3).

The rectifying and smoothing circuit 211 is a circuit that generates DCpower by rectifying and smoothing electric power (AC power) suppliedfrom the power reception section 210.

The voltage stabilizing circuit 212 is a circuit that performspredetermined voltage stabilization operation based on the DC powersupplied from the rectifying and smoothing circuit 211, thereby charginga battery (not illustrated) in the load 22. It is to be noted that sucha battery is configured using, for example, a chargeable battery (asecondary battery) such as a lithium ion battery.

The capacitor C2 is disposed to be connected to the power reception coilL2 electrically in parallel or in a combination of parallel and series.

[Detailed Configuration of Elements Including High-Frequency PowerGeneration Circuit 112 and Current-Voltage Detection Section 113]

FIG. 3 is a circuit diagram illustrating a detailed-configurationexample of the power transmission section 110, the capacitor C1, thehigh-frequency power generation circuit 112, the current-voltagedetection section 113 (the current detection section 113I and thevoltage detection section 113V), the power reception section 210, andthe capacitor C2.

The power transmission section 110 has the power transmission coil L1,and the power reception section 210 has the power reception coil L2. Thepower transmission coil L1 is the coil used to perform the electricpower transmission using the magnetic field (to cause the magneticflux), as described above. On the other hand, the power reception coilL2 is the coil used to receive the electric power transmitted from thepower transmission section 110 (from the magnetic flux).

The high-frequency power generation circuit 112 is the circuit thatgenerates the high-frequency electric power (the AC signal) made of anAC voltage Vac and an alternating current Iac based on a DC voltage Vdc(a direct current Idc) supplied from the power circuit 111. Here, thishigh-frequency power generation circuit 112 is configured using aswitching amplifier (a so-called class E amplifier) including a singletransistor 112T as a switching element. This switching amplifierincludes a capacitor 112C used for ripple removal, a coil 112L servingas a choke coil, and the transistor 112T that is an N-type FET (FieldEffective Transistor). One end of the capacitor 112C is connected to anoutput line from the power circuit 111 as well as one end of the coil112L, and the other end is grounded. The other end of the coil 112L isconnected to a drain of the transistor 112T and one end of each ofcapacitors C1 p and C1 s at a connection point P21. A source of thetransistor 112T is grounded, and to a gate, the control signal CTLsupplied from the control section 114 as described above is inputted. Itis to be noted that the other end of the capacitor C1 s is connected toone end of the power transmission coil L1, and the other end of thecapacitor C1 p is grounded. Based on such a configuration, thehigh-frequency electric power described above is generated in thehigh-frequency power generation circuit 112 by causing the transistor112T to perform ON/OFF operation (switching operation including apredetermined switching frequency and a predetermined duty ratio)according to the control signal CTL.

The current detection section 113I is a circuit that detects the currentI1 (the alternating current) described above, and here, is disposedbetween the other end of the power transmission coil L1 and a ground.This current detection section 113I includes a resistance R11, anamplifier A1, a diode D1, and a capacitor C31. The resistance R11 isdisposed between the other end (a connection point P22) of the powertransmission coil L1 and the ground. As for the amplifier A1, one inputterminal is connected to the connection point P22, the other inputterminal is connected to the ground, and an output terminal is connectedto an anode of the diode D1. In other words, a potential differencebetween both ends of the resistance R11 is inputted into this amplifierA1. A cathode of the diode D1 is connected to one end (a connectionpoint P23) of the capacitor C31, and the other end of the capacitor C31is grounded. Based on such a configuration, in the current detectionsection 113I, a detection result of the current I1 (the alternatingcurrent) described above is outputted from the cathode side (theconnection point P23) of the diode D1.

The voltage detection section 113V is a circuit that detects the voltageV1 (the AC voltage) described above, and here, is disposed between theconnection point P21 and the ground. This voltage detection section 113Vhas resistances R21 and R22, an amplifier A2, a diode D2, and acapacitor C32. One end of the resistance R21 is connected to theconnection point P21, and the other end is connected to a connectionpoint P24. One end of the resistance R22 is connected to the connectionpoint P24, and the other end is connected to the ground. As for theamplifier A2, one input terminal is connected to the connection pointP24, the other input terminal is connected to the ground, and an outputterminal is connected to an anode of the diode D2. A cathode of thediode D2 is connected to one end (a connection point P25) of thecapacitor C32, and the other end of the capacitor C32 is grounded. Basedon such a configuration, in the voltage detection section 113V, adetection result of the voltage V1 (the AC voltage) described above isoutputted from the cathode side (the connection point P25) of the diodeD2.

One end of a capacitor C2 p is connected to one end of the powerreception coil L2 at a connection point P26, and the other end isconnected to the other end of the power reception coil L2 at aconnection point P27. One end of a capacitor C2 s is connected to theconnection point P26, and the other end is connected to one inputterminal of the rectifying and smoothing circuit 211. It is to be notedthat the other input terminal of the rectifying and smoothing circuit211 is connected to the connection point P27.

[Operation and Effects of Feed System 4]

(1. Summary of Overall Operation)

In this feed system 4, the predetermined high-frequency electric power(the AC signal) for the electric power transmission is supplied to thepower transmission coil L1 and the capacitor C1 in the powertransmission section 110 by the high-frequency power generation circuit112, in the feed unit 1. This causes the magnetic field (the magneticflux) in the power transmission coil L1 in the power transmissionsection 110. At this moment, when the electronic devices 2A and 2B eachserving as the device to be power-supplied (the device to be charged)are placed on (or brought close to) the top surface (the feeding surfaceS1) of the feed unit 1, the power transmission coil L1 in the feed unit1 and the power reception coil L2 in each of the electronic devices 2Aand 2B are in proximity to each other in the vicinity of the powerfeeding surface S1.

In this way, when the power reception coil L2 is placed in proximity tothe power transmission coil L1 producing the magnetic field (themagnetic flux), an electromotive force is evoked in the power receptioncoil L2 by the magnetic flux produced by the power transmission coil L1.As a result, electric power is transmitted from the power transmissioncoil L1 side (a primary side, the feed unit 1 side, and the powertransmission section 110 side) to the power reception coil L2 side (asecondary side, the electronic devices 2A and 2B side, and the powerreception section 210 side) (see electric power P1 illustrated in FIG. 2and FIG. 3).

Then, in the electronic devices 2A and 2B, the AC power received by thepower reception coil L2 is supplied to the rectifying and smoothingcircuit 211 and the voltage stabilizing circuit 212, and the followingcharging operation is performed. That is, after this AC power isconverted into predetermined DC power by the rectifying and smoothingcircuit 211, the voltage stabilization operation based on this DC poweris performed by the voltage stabilizing circuit 212, and the battery(not illustrated) in the load 22 is charged. In this way, in theelectronic devices 2A and 2B, the charging operation based on theelectric power received by the power reception section 210 is performed.

In other words, in the present embodiment, at the time of charging theelectronic devices 2A and 2B, terminal connection to an AC adapter orthe like, for example, is unnecessary, and it is possible to start thecharge easily by merely placing the electronic devices 2A and 2B on (orbringing the electronic devices 2A and 2B close to) the power feedingsurface S1 of the feed unit 1 (noncontact power feeding is performed).This leads to a reduction in burden on a user. Further, this noncontactpower feeding has advantages including preventing characteristicdeterioration due to abrasion of contacts and no concern about anelectric shock due to touching a contact by a person. Furthermore, thereis also such an advantage that it is possible to prevent a contact fromcorroding by becoming wet, in a case of application to, for example, adevice used in a wet environment, such as a toothbrush or a shaver.

(2.2 Operation Including Detection Operation of Secondary-Side Device)

Next, operation (detection operation and the like of the electronicdevices 2A and 2B (the secondary-side devices) each serving as thedevice to be power-supplied) in the feed unit 1 (the power transmissionunit 11) of the present embodiment will be described with reference toFIG. 4 to FIG. 10. FIG. 4 is a flowchart illustrating an example of thisoperation in the feed unit 1.

First, the feed unit 1 performs predetermined activation processing suchas initialization of a control terminal (not illustrated), for example(step S101).

Then, the current-voltage detection section 113 (the current detectionsection 113I and the voltage detection section 113V) detects thealternating current (the current I1) and the AC voltage (the voltage V1)in the vicinity of the power transmission section 110 (on the load sideof the high-frequency power generation circuit 112), respectively, bythe technique described above (step S102).

Next, the control section 114 calculates impedance Z1 (the loadimpedance of the high-frequency power generation circuit 112 (theswitching amplifier); see FIG. 3) in the vicinity of the powertransmission section 110 by using the current I1 and the voltage V1detected by the current-voltage detection section 113 (step S103).Specifically, it is possible to determine an absolute value |Z1| of thisimpedance Z1 by the following expression (1).|Z1|=(V1/I1)  (1)

Subsequently, through use of a change in the impedance Z1 calculated asdescribed above, whether the secondary-side device (the electronicdevices 2A and 2B) serving as the device to be power-supplied is inproximity or not is detected by the control section 114 as follows.

Here, it is desirable that, specifically, such detection of the deviceto be power-supplied be performed intermittently at a predeterminedinterval (a non-detection period (a detection stop period) Ts), asillustrated in FIG. 5, for example. This is because performing suchdetection constantly increases power consumption for the detectionoperation. However, when this non-detection period Ts is set to belonger than necessary, time for the detection of the device to bepower-supplied tends to become longer as well and therefore, it isnecessary to set the non-detection period Ts appropriately. It may besaid that, by taking account of a balance between these facts, it isdesirable that the interval (the non-detection period Ts) between thedetection periods (the detection periods Td) of detecting the device tobe power-supplied be freely controllable manually or automatically, forexample.

The detection of the device to be power-supplied (the secondary-sidedevice) by the control section 114 described above is specificallyperformed as follows. That is, at first, as indicated by a sign G0 inFIG. 6A, for example, the frequency characteristics of the absolutevalue |Z1| of the impedance Z1 exhibits a peak at a resonance frequencyf0 when the secondary-side device is not in proximity (is absent). Here,this resonance frequency f0 may be expressed by the followingexpressions (2) and (3).f0=1/{2π×√(L1×C1)}  (2)C1=(C1s×C1p)/(C1s+C1p)  (3)

On the other hand, as indicated by arrows P3L and P3H as well as a signG1 in FIG. 6A, the frequency characteristics of the absolute value |Z1|of the impedance Z1 exhibit a so-called double hump characteristics whenthe secondary-side device is in proximity (is present). In other words,a peak is exhibited at each of a frequency f1H on a high frequency sideand a frequency f1L on a low frequency side, of the resonance frequencyf0. For this reason, a variation ΔZ (a variation from the time when thesecondary-side device is absent to the time when the secondary-sidedevice is present) in the absolute value |Z1| of the impedance Z1 is apositive value (ΔZ>0) at frequencies in the neighborhood of thefrequency f1H and the frequency f1L, as illustrated in FIG. 6A, forexample.

Using this, the control section 114 determines the presence or absenceof the device to be power-supplied, based on an increment (the variationΔZ) in the absolute value |Z1| of the impedance Z1. Specifically, thecontrol section 114 determines the presence or absence of the device tobe power-supplied by comparing the variation ΔZ (>0) in the impedancewith a predetermined threshold ΔZth (step S104). In other words, whenthis variation ΔZ (the increment) is greater than the threshold ΔZth(ΔZ>ΔZth) (step S104: Y), it is determined that the secondary-sidedevice (the device to be power-supplied) is in proximity (is present)(step S106). On the other hand, when this variation ΔZ (the increment)is equal to or less than the threshold ΔZth (ΔZ≤ΔZth) (step S104: N), itis determined that the secondary-side device (the device to bepower-supplied) is not in proximity (is absent) (step S105).

At this moment, it is also possible to distinguish between the presenceand absence of a foreign object (metallic foreign object) different fromthe device to be power-supplied. In other words, as indicated by signsG0 and G2 as well as an arrow P4 in FIG. 6B, for example, in a casewhere a metallic foreign object exists (is present) in proximity to thefeed unit 1 (the feeding surface S1), the absolute value |Z1| of theimpedance Z1 tends to decrease, as compared with a case where a metallicforeign object does not exist (is absent). This is because an eddycurrent is produced in the metallic foreign object, resulting in a lossof electric power. Therefore, it is possible to determine the presenceor absence of such a foreign object according to whether the absolutevalue |Z1| of the impedance Z1 exhibits an increasing change or adecreasing change (whether the variation ΔZ is a positive value or anegative value) at frequencies in the neighborhood of the frequenciesf1H and f1L described above, for example. This makes it possible toavoid applying electric power to the power transmission coil L1wastefully, and also to evade fears such as heat generation of themetallic foreign object.

It is to be noted that the value of the absolute value |Z1| of theimpedance Z1 in the vicinity of the frequencies f1H and f1L when thesecondary-side device is placed in proximity to the primary-side devicedepends on the magnitude of a Q value in a resonance circuit of thesecondary-side device. In other words, the higher this Q value is, thegreater the value of the absolute value |Z1| is, and therefore, it maybe said that, desirably, the load of the secondary-side device is ahighest possible resistance value at the time of the detectionoperation.

Here, it is desirable that the control section 114 control one or bothof a frequency CTL(f) and a duty ratio CTL(D) in the control signal CTL,thereby adjusting the variation ΔZ in the absolute value |Z1| of theimpedance Z1. This is because detectability is enhanced by setting thedifference (the variation ΔZ) in |Z1| between the time when the deviceto be power-supplied is present and the time when it is absent to be aslarge as possible (maximum), like the frequencies in the vicinity of thefrequencies f1H and f1L described above.

Specifically, the control section 114 controls the frequency CTL(f) inthe control signal CTL to become a frequency in the vicinity of thefrequencies f1H and f1L, as illustrated in FIG. 6A, for example.

In addition, as illustrated in Parts (A) and (B) of FIG. 7, for example,the control section 114 controls the duty ratio CTL(D) in the controlsignal CTL so that the variation ΔZ in the absolute value |Z1| of theimpedance Z1 becomes as large as possible. This control is performedusing the following phenomena. That is, for example, as indicated bysigns P51 and P52 in FIGS. 8A and 8B, there is a difference in terms ofthe magnitude of a harmonic component in the absolute value |Z1| of theimpedance Z1, between a case where the duty ratio CTL(D)=about 50% whichis relatively high (corresponding to Part (A) of FIG. 7) and a casewhere the duty ratio CTL(D)=about 10% which is relatively low(corresponding to Part (B) of FIG. 7). Therefore, it is desirable thatthe control section 114 adjust the variation ΔZ by taking account of thefact that the magnitude of the harmonic component in the absolute value|Z1| of the impedance Z1 changes in response to a change in the dutyratio CTL(D), as indicated by signs G3L and G3H as well as arrows P5Land P5H in FIG. 9, for example.

Here, when it is determined that the secondary-side device is inproximity in step S106, predetermined device authentication is thenperformed for the secondary-side device (the electronic devices 2A and2B) by the feed unit 1 (step S107), for example. Subsequently, the feedunit 1 performs the noncontact feeding operation described above,thereby charging the electronic devices 2A and 2B which are the devicesto be power-supplied (step S108). In other words, the power transmissionsection 110 starts the electric power transmission to the device to bepower-supplied after the device to be power-supplied is detected. Inthis feeding operation, specifically, a feeding period Tp and acommunication period Tc (a period in which predetermined communicationoperation is performed between the primary-side device and thesecondary-side device) are provided time-divisionally and periodically,as illustrated in FIG. 10, for example.

Subsequently, the feed unit 1 determines whether or not to terminatewhole processing illustrated in FIG. 4, for example (step S109). Here,when it is determined that the whole processing is not to be terminatedyet (step S109: N), the feed unit 1 then determines whetherpredetermined time that is set beforehand has elapsed (step S110), forexample. When it is determined that the predetermined time has notelapsed yet (step S110: N), the flow returns to step S108 to continuethe power feeding operation. On the other hand, when it is determinedthat the predetermined time has elapsed (step S110: Y), the flow returnsto step S102 to perform the detection operation of the secondary-sidedevice. In this way, it is desirable that the current-voltage detectionsection 113 and the control section 114 perform the detection of thedevice to be power-supplied periodically also after the electric powertransmission is started.

It is to be noted that when it is determined that the whole processingis to be terminated (step S109: Y), the operation (whole processing) inthe feed unit 1 illustrated in FIG. 4 ends.

In this way, in the present embodiment, whether the device to besupplied with the power by the power transmission section 110 is inproximity or not is detected using the change in the impedance Z1 in thevicinity of the power transmission section 110. This makes it possibleto perform the detection of the device to be power-supplied withoutcomplicating the configuration, the technique, and the like, forexample.

In the present embodiment as described above, whether the device to besupplied with the power by the power transmission section 110 is inproximity or not is detected using the change in the impedance Z1 in thevicinity of the power transmission section 110 and thus, it is possibleto perform the detection of the device to be power-supplied withoutcomplicating the configuration, the technique, and the like, forexample. Therefore, it is possible to detect the device to bepower-supplied conveniently when the electric power transmission isperformed using the magnetic field. This makes it possible to detect thedevice to be power-supplied even when a coefficient of coupling betweenthe power transmission coil L1 and the power reception coil L2 is low,about 0.4 or less, for example.

Further, for instance, addition of a magnet and a circuit such as amagnetic sensor is unnecessary and thus, it is possible to reduce thecost and size, and also a frequency for the detection is allowed to beset freely. Therefore, for example, application to circuits other than aself-excited oscillation circuit is possible.

It is to be noted that the current-voltage detection section 113 may notbe provided in a case where a circuit detecting a current or a voltageis already provided in a feed unit for the purpose of measuring its ownpower consumption, for example. In that case, additional hardware isunnecessary.

Second Embodiment

Next, the second embodiment of the disclosure will be described. It isto be noted that the same elements as those of the first embodiment willbe provided with the same characters as those of the first embodiment,and the description will be omitted as appropriate.

[Overall Configuration of Feed System 4A]

FIG. 11 illustrates an example of an overall block configuration of afeed system (a feed system 4A) according to the second embodiment. Thefeed system 4A of the present embodiment also is a feed system thatperforms noncontact electric power transmission using a magnetic field,and includes a feed unit 1A (a primary-side device) and one or moreelectronic devices (here, two electronic devices 2A and 2B;secondary-side devices) each serving as a device to be power-supplied.In other words, this feed system 4A includes the feed unit 1A in placeof the feed unit 1 in the feed system 4 of the first embodiment, and isotherwise similar in configuration to the feed system 4.

(Feed Unit 1A)

The feed unit 1A performs the electric power transmission to theelectronic devices 2A and 2B using the magnetic field in a mannersimilar to the feed unit 1. This feed unit 1A includes a powertransmission unit 11A having a power transmission section 110, a powercircuit 111, a high-frequency power generation circuit 112, acurrent-voltage detection section 113A, a control section 114, and acapacitor C1. In other words, this power transmission unit 11A isprovided with the current-voltage detection section 113A in place of thecurrent-voltage detection section 113 in the power transmission unit 11described in the first embodiment. It is to be noted that thecurrent-voltage detection section 113A and the control section 114correspond to a specific example of a “detection section” of thedisclosure.

The current-voltage detection section 113A detects a direct current (acurrent I2) and a DC voltage (a voltage V2) in the vicinity of the powertransmission section 110, instead of the alternating current (thecurrent I1) and the AC voltage (the voltage V1) described in the firstembodiment. The current I2 and the voltage V2 correspond to a directcurrent and a DC voltage to be supplied from the power circuit 111 tothe high-frequency power generation circuit 112, respectively.

Then, in the control section 114 of the present embodiment, instead ofthe impedance Z1 described in the first embodiment, a DC resistancevalue R2 determined based on the direct current (the current I2) and theDC voltage (the voltage V2) is used as impedance in the vicinity of thepower transmission section 110. This DC resistance value R2 isdetermined by the following expression (4).R2=(V2/I2)  (4)[Operation and Effects of Feed System 4A]

Specifically, for example, as in an operation example of the feed unit1A (the power transmission unit 11A) of the present embodimentillustrated in FIG. 12, the control section 114 uses the DC resistancevalue R2 described above, a variation ΔR thereof, and a threshold ΔRththereof, instead of the absolute value |Z1| of the impedance Z1described in the first embodiment, the variation ΔR thereof, and thethreshold ΔRth thereof (steps S202 to S204).

Here, electric power consumed in or after the high-frequency powergeneration circuit 112 (a switching amplifier) is determined based onthis DC resistance value R2. On the other hand, an increase in theimpedance Z1 reduces a current flowing into the power transmissionsection 110 and therefore, power consumption in the power transmissionsection 110 is reduced, and as a result, the DC resistance value R2 isincreased. For this reason, it is possible to determine the presence orabsence of the secondary-side device by judging the magnitude of the DCresistance value R2, like the case of the impedance Z1.

At this moment, when power consumption except the one in the powertransmission section 110 is large, a tendency of the impedance Z1 and atendency of the DC resistance value R2 disagree with each other,reducing accuracy of detecting the secondary-side device. Most of suchpower consumption except the one in the power transmission section 110is a loss by a coil 112L and a switching element (a transistor 112T). Inorder to reduce the electric power loss by these, it is conceivable toperform driving with a high DC voltage to reduce the ratio of a current,or to shorten an ON period of the switching element by reducing adriving duty ratio of the switching amplifier, besides selecting alow-loss element.

In this way, it is possible to obtain similar effects by similaroperation to those of the first embodiment, in the present embodiment aswell. In other words, it is possible to detect the device to bepower-supplied conveniently when performing the electric powertransmission using the magnetic field.

It is to be noted that the current-voltage detection section 113A maynot be provided in some cases, and in that case, additional hardware isunnecessary in the present embodiment as well.

[Modifications]

Next, modifications (modifications 1 to 6) common to the first andsecond embodiments will be described. It is to be noted that the sameelements as those of these embodiments will be provided with the samecharacters as those of these embodiments, and the description thereofwill be omitted as appropriate.

[Modifications 1 and 2]

FIG. 13A is a timing chart illustrating detection periods Td1 and Td2 aswell as the non-detection period Ts according to the modification 1, andFIG. 13B is a timing chart illustrating the detection periods Td1 andTd2 as well as the non-detection period Ts according to the modification2. In these modifications 1 and 2, a plurality of kinds of value (here,two kinds; frequencies f1 and f2) are used for the frequency (CTL(f)) inthe control signal CTL, as will be described below. In other words, thecontrol section 114 adjusts the variation in the impedance by using theplurality of kinds of value for the frequency (CTL(f)) in the controlsignal CTL.

Specifically, in the modification 1 illustrated in FIG. 13A, the controlsection 114 sequentially uses the two kinds of value (the frequencies f1and f2) one by one during the detection period of detecting the deviceto be power-supplied (a period corresponding to the detection periodsTd1 and Td2 as a whole). This makes it possible to shorten the time forthe detection relatively as compared with a technique in FIG. 13B whichwill be described below.

In the modification 2 illustrated in FIG. 13B on the other hand, thecontrol section 114 selectively uses one of the two kinds of value (thefrequencies f1 and f2), for every detection period of detecting thedevice to be power-supplied (for each of the detection periods Td1 andTd2). This makes it possible to reduce the power consumption in thedetection operation relatively as compared with the technique of FIG.13A described above.

[Modifications 3 and 4]

FIG. 14A is a timing chart illustrating detection periods Td1 and Td3 aswell as the non-detection period Ts according to the modification 3, andFIG. 14B is a timing chart illustrating the detection periods Td1 andTd3 as well as the non-detection period Ts according to the modification4. In these modifications 3 and 4, a plurality of kinds of value (here,two kinds of duty ratio; Duty1 and Duty2) are used for the duty ratio(CTL(D)) in the control signal CTL, as will be described below.

Specifically, in the modification 3 illustrated in FIG. 14A, the controlsection 114 sequentially uses the two kinds of value (the duty ratiosDuty1 and Duty2) one by one in the detection period of detecting thedevice to be power-supplied (the detection periods Td1 and Td3). Thismakes it possible to shorten the time for the detection relatively ascompared with a technique of FIG. 14B which will be described below.

In the modification 4 illustrated in FIG. 14B on the other hand, thecontrol section 114 selectively uses one of the two kinds of value (theduty ratios Duty1 and Duty2) for every detection period of detecting thedevice to be power-supplied (for each of the detection periods Td1 andTd3). This makes it possible to reduce the power consumption in thedetection operation relatively as compared with the technique of FIG.14A described above.

[Modifications 5 and 6]

FIG. 15A is a timing chart illustrating detection periods Td1 and Td4 aswell as the non-detection period Ts according to the modification 5, andFIG. 15B is a timing chart illustrating the detection periods Td1 andTd4 as well as the non-detection period Ts according to the modification6. In these modifications 5 and 6, a plurality of kinds of value (here,the two kinds of frequency; f1 and f2, and the two kinds of duty ratio;Duty1 and Duty2) are used for both of the frequency (CTL(f)) and theduty ratio (CTL(D)) of the control signal CTL, as will be describedbelow. In other words, in these modifications 5 and 6, the modifications1 and 2 are combined with the modifications 3 and 4.

Specifically, in the modification 5 illustrated in FIG. 15A, the controlsection 114 uses sequentially the two kinds of value (the frequencies f1and f2 as well as the duty ratios Duty1 and Duty2) one by one during thedetection period of detecting the device to be power-supplied (thedetection periods Td1 and Td4). This makes it possible to shorten thetime for the detection relatively as compared with a technique of FIG.15B which will be described below.

In the modification 6 illustrated in FIG. 15B on the other hand, thecontrol section 114 selectively uses by one of the two kinds of value(the frequencies f1 and f2 as well as the duty ratios Duty1 and Duty2),for every detection period of detecting the device to be power-supplied(for each of the detection periods Td1 and Td4). This makes it possibleto reduce the power consumption in the detection operation relatively ascompared with the technique of FIG. 15A described above.

[Other Modifications]

The technology of the disclosure has been described using someembodiments and modifications, but is not limited to these embodimentsand modifications, and may be variously modified.

For example, in the embodiments and modifications, the description hasbeen provided specifically using the configuration of the high-frequencypower generation circuit, although it is not limited thereto. Forexample, a configuration employing a half-bridge circuit or afull-bridge circuit may be provided.

Further, in the embodiments and modifications, the description has beenprovided specifically using the configuration of the current-voltagedetection section and the detection operation, although it is notlimited thereto. Other configuration and detection operation may beemployed.

Furthermore, in the embodiments and modifications, the description hasbeen provided by taking the electronic device as an example of thedevice to be power-supplied, although it is not limited thereto. Devicesto be power-supplied other than the electronic devices may be used (forexample, vehicles such as electric cars).

In addition, in the embodiments and modifications, the description hasbeen provided specifically using the configuration of each of thefeeding unit and the device to be power-supplied (the electronic deviceetc.). However, it is not necessary to provide all the elements, andother configuration may be further provided. For instance, a battery forcharge may be provided also in the power reception unit 21 in somecases.

Moreover, in the embodiments and modifications, the description has beenprovided by taking the case where the plurality of (two) devices to bepower-supplied (electronic devices) are provided in the feed system asan example, although it is not limited thereto. Only one device to bepower-supplied may be provided in the feed system.

Furthermore, in the embodiments and modifications, the description hasbeen provided by taking the charging tray for the small electronicdevices (CE devices) such as portable telephones as an example of thefeed unit. However, the feed unit is not limited to such a home chargingtray, and is applicable to chargers for various devices to bepower-supplied (electronic devices etc.). In addition, the feed unit maynot be a tray, and may be a stand for an electronic device such as aso-called cradle, for example.

It is possible to achieve at least the following configurations from theabove-described example embodiments and the modifications of thedisclosure.

(1) A device for power transmission comprising:

a power transmission section configured to transmit an electric powerwirelessly; and

a detection section operatively connected to the power transmissionsection and configured to detect an object within a range from the powertransmission section based on a change in impedance in vicinity of thepower transmission section.

(2) The device of (1), further comprising a power generation circuitoperatively connected to the power transmission section and configuredto generate the electric power.

(3) The device of (2), wherein the electric power is a high-frequencyelectric power.

(4) The device of (2), wherein the detection section comprises:

a current-voltage detection unit configured to detect a current and avoltage in vicinity of the power transmission section; and

a control unit operatively connected to the current-voltage detectionunit and configured to detect the object based on the change inimpedance calculated by the detected current and voltage in vicinity ofthe power transmission section.

(5) The device of (4), wherein the detected current is an alternatingcurrent and the detected voltage is an AC voltage.

(6) The device of (4), wherein:

the detected current is a direct current and the detected voltage is aDC voltage; and

the change in impedance is a change in resistance calculated by thedirect current and the DC voltage.

(7) The device of (1), wherein the detection section is configured todetermine whether the detected object is a device to be power-suppliedby the power transmission section or a foreign object based on whetherthe impedance increases or decreases.

(8) The device of (7), wherein the determination is made based onwhether an absolute value of the impedance increases or decreases.

(9) The device of (7), wherein the determination is made based onwhether a resistance value increases or decreases.

(10) The device of (7), wherein the detected object is a device to bepower-supplied by the power transmission section if the impedanceincreases.

(11) The device of (7), wherein the detected object is a foreign objectif the impedance decreases.

(12) The device of (1), wherein the detection section is configured todetect the object intermittently at an interval.

(13) The device of (1), wherein the detection section is configured todetect the object by comparing the change in impedance with a thresholdvalue.

(14) The device of (4), wherein the control section is configured tosequentially provide two control signals during each detection periodfor detecting the object, the two control signals having a same dutyratio but different frequencies.

(15) The device of (4), wherein the control section is configured tosequentially provide two control signals for each two subsequentdetection periods for detecting the object, the two control signalshaving a same duty ratio but different frequencies.

(16) The device of (4), wherein the control section is configured tosequentially provide two control signals during each detection periodfor detecting the object, the two control signals having a samefrequency but different duty ratios.

(17) The device of (4), wherein the control section is configured tosequentially provide two control signals for each two subsequentdetection periods for detecting the object, the two control signalshaving a same frequency but different duty ratios.

(18) The device of (4), wherein the control section is configured tosequentially provide two control signals during each detection periodfor detecting the object, the two control signals having different dutyratios and different frequencies.

(19) The device of (4), wherein the control section is configured tosequentially provide two control signals for each two subsequentdetection periods for detecting the object, the two control signalshaving different duty ratios and different frequencies.

(20) The device of (4), wherein the control section is configured tocontrol at least one of a frequency and a duty ratio in the controlsignal to adjust the change in impedance.

(21) A system for power transmission comprising:

a transmitting device comprising (a) a power transmission sectionconfigured to transmit an electric power wirelessly, and (b) a detectionsection operatively connected to the power transmission section andconfigured to detect a receiving device within a range from the powertransmission section based on a change in impedance in vicinity of thepower transmission section; and

a receiving device comprising (c) a power reception unit configured toreceive the electric power wirelessly, and (d) a load operativelyconnected to the power reception unit and configured to perform anoperation based on the received electric power.

(22) The system of (21), wherein the transmitting device furthercomprises a power generation circuit operatively connected to the powertransmission section and configured to generate the electric power.

(23) The system of (22), wherein the detection section comprises:

a current-voltage detection unit configured to detect a current and avoltage in vicinity of the power transmission section; and

a control unit operatively connected to the current-voltage detectionunit and configured to detect the object based on the change inimpedance calculated by the detected current and voltage in vicinity ofthe power transmission section.

(24) A method for detecting an object comprising:

detecting a current and a voltage in vicinity of a power transmittingdevice;

calculating an impedance based on the detected current and voltage; and

detecting an object within a range from the power transmitting devicebased on a change in the impedance.

(25) The method of (24), further comprising determining whether thedetected object is a power receiving device to be power-supplied by thepower transmission device or a foreign object based on whether theimpedance increases or decreases.

(26) The method of (25), wherein the determination is made based onwhether an absolute value of the impedance increases or decreases.

(27) The method of (25), wherein the determination is made based onwhether a resistance value increases or decreases.

(28) The method of (25), wherein the detected object is a powerreceiving device if the impedance increases.

(29) The method of (25), wherein the detected object is a foreign objectif the impedance decreases.

(30) The method of (24), further comprising comparing the change in theimpedance with a threshold value.

(31) The method of (24), wherein the object is detected intermittentlyat an interval.

(32) The method of (25), further comprising, in response to determiningthat the detected object is a power receiving device, transmitting anelectric power wirelessly from the power transmitting device to thepower receiving device.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A power transmitter, comprising: a powertransmission section configured to transmit an electric powerwirelessly, to a power receiver, wherein the power transmission sectioncomprises a coil; a resistor mounted in series with the coil; and adetection section configured to: measure a first voltage across theresistor; and detect a foreign object within a range from the powertransmission section based on the first voltage, wherein a frequency ofa second voltage across the resister is different from a frequency ofthe first voltage, the power transmission section transmits the electricpower at the frequency of the second voltage, and the detection sectionmeasures the first voltage at the frequency of the first voltage.
 2. Thepower transmitter of claim 1, wherein the detection section is furtherconfigured to detect the foreign object intermittently at an interval.3. The power transmitter of claim 1, wherein the detection section isfurther configured to: compare the first voltage with a threshold value;and detect the foreign object based on a result of the comparison. 4.The power transmitter of claim 1, wherein the detection section isfurther configured to: calculate impedance within the range from thepower transmission section based on the first voltage; and detect theforeign object based on the impedance.
 5. The power transmitter of claim4, wherein the detection section is further configured to: compare theimpedance with a threshold value; and detect the foreign object based ona result of the comparison.
 6. The power transmitter of claim 1, whereinthe power transmission section further comprises a capacitor connectedto the coil electrically one of in parallel, in series, or in acombination of parallel and series.
 7. The power transmitter of claim 1,wherein the detection section is further configured to detect theforeign object based on a change in a load impedance of a powergeneration circuit.
 8. The power transmitter of claim 7, furthercomprising the power generation circuit operatively connected to thepower transmission section, wherein the power generation circuit isconfigured to generate the electric power.
 9. The power transmitter ofclaim 7, wherein the detection section comprises: a current-voltagedetection unit configured to detect a current and a voltage within therange from the power transmission section; and a control sectionoperatively connected to the current-voltage detection unit, wherein thecontrol section is configured to: calculate the change in the loadimpedance based on the detected current and the detected voltage; anddetect the foreign object based on the calculated change in the loadimpedance.
 10. The power transmitter of claim 1, wherein the detectionsection is further configured to detect a device to be power-supplied bythe power transmission section, and the device to be power-supplied isdetected based on the first voltage.
 11. A method, comprising: in apower transmitter: transmitting an electric power wirelessly to a powerreceiver through a coil; measuring a first voltage across a resistormounted in series with the coil; and detecting a foreign object within arange from the power transmitter based on the first voltage, wherein afrequency of a second voltage across the resistor is different from afrequency of the first voltage, the electric power is transmitted at thefrequency of the second voltage, and the first voltage is measure at thefrequency of the first voltage.
 12. The method of claim 11, furthercomprising detecting the foreign object intermittently at an interval.13. The method of claim 11, further comprising detecting the foreignobject based on a change in a load impedance of a power generationcircuit.
 14. The method of claim 11, further comprising detecting, basedon the first voltage, a device to be power-supplied.
 15. A power feedingsystem, comprising: a power transmitter comprising: a power transmissionsection configured to transmit an electric power wirelessly to a powerreceiver, wherein the power transmission section comprises a coil; aresistor mounted in series with the coil; and a detection sectionconfigured to: measure a first voltage across the resistor; and detect aforeign object within a range from the power transmission section basedon the first voltage, a frequency of a second voltage across theresistor is different from a frequency of the first voltage, the powertransmission section transmits the electric power at the frequency ofthe second voltage, and the detection section measures the first voltageat the frequency of the first voltage; and the power receivercomprising: a power reception section configured to receive the electricpower wirelessly; and a load operatively connected to the powerreception section, wherein the load is configured to perform anoperation based on the received electric power.